Accessory Flexor Digitorum Superficialis Indicis as Likely Cause of Recalcitrant Carpal Tunnel Syndrome: A Case Report.

CASE: A 35-year-old woman with prior bilateral open carpal tunnel release presented with recurrent right-hand pain, numbness, tingling, nocturnal awakening, and weakness. Examination showed positive Phalen compression and Tinel signs at the carpal tunnel. Electrodiagnostic testing revealed mild median neuropathy, and ultrasonography demonstrated a bifid median nerve with focal enlargement. Revision exploration identified an accessory flexor digitorum superficialis (FDS) indicis muscle within the carpal tunnel. Repeat decompression, muscle excision, and hypothenar fat flap coverage resulted in resolution of symptoms at 5 months postrevision surgery. CONCLUSION: Accessory FDS indicis is a rare but possible structural cause of recalcitrant carpal tunnel syndrome.